To form timepiece dials it is known to deposit a layer of enamel on the visible surface thereof to considerably improve the quality of their appearance.
FIG. 1 shows an example timepiece 1, whose dial 3 includes most of the manufacturing pitfalls that may be encountered. Dial 3 thus includes a main plane P forming the broadest visible face.
As seen in FIG. 1, above plane P, dial 3 may have fitted thereon an hour circle 2 and/or a secondary display 4 formed by at least one index and/or at least one alphanumerical symbol.
Dial 3 may also include a secondary display 5 whose visible surface is mounted along a plane P+1 above plane P so as to form a raised zone. Conversely, dial 3 may also include a secondary display 6 whose visible surface is mounted along a plane P−1 underneath plane P so as to form a recessed or hollow area. Dial 3 may also include an aperture 7, i.e. an opening in dial 3 for showing part of movement 8 mounted underneath dial 3, like a moon phase in the example in FIG. 1.
Finally, dial 3 also includes holes allowing a member of movement 8 to pass through dial 3, such as for example arbours for mounting the hands of timepiece 1.
The example illustrated in FIG. 2 partially shows a known embodiment of enamelled dial 3 which includes a secondary display 6 which is mounted in a plane P−1 underneath plane P so as to form a hollow or recessed area 9. Area 9 is intended to receive, for example, the graduations and display hand via hole 10.
FIG. 2 shows that dial 3 is formed by a base 13 including feet 14 and on which a first enamelled, pierced plate 15 is mounted, the visible surface of which forms plane P. Dial 3 also includes a second enamelled plate 17, which is mounted in the pierced hole in first plate 15 forming an interstice 16 and whose visible face forms a lower, hollow or recessed plane P−1.
This configuration advantageously provides a totally enamelled dial 3 since only enamelled plates 15 and 17 are visible. However, this configuration requires a very high level of precision for the dimensions of plates 15 and 17 to make the visual rendering of interstice 16 acceptable. Indeed, the external wall of plate 17 must be a perfect, regular fit for the wall of the pierced hole made in plate 15 otherwise continuous or odd gaps may appear which makes dial 3 visually unacceptable for integration in a timepiece 1.
Consequently, the embodiment of FIG. 2 leads to an excessively high reject rate and a requirement for manufacturing precision that only further increase the manufacturing cost of enamelled dials, which are already very high for structural reasons.